1. Field of the Invention
This invention relates to a calcium phosphate type composition for coating bioceramics, a method for coating bioceramics, and composite bioceramics produced as a result of the coating. The composite bioceramics possess high strength and excel in bio-affinity and, therefore, prove to be useful as artificial bones, for example.
2. Prior Art Statement
Such ceramics as sapphire and sintered alumina possess high strength and manifest no toxicity in living organisms and efforts are being made to promote their use as bioceramics as artificial tooth roots, artificial bones and the like. These materials have a disadvantage in that since they are inert to vital tissues, they are incapable of binding themselves with neoplastic bones and are susceptible to "obvelation", i.e. of being enveloped in fibrous tissues by the living organism. Therefore, they cannot be kept implanted for a long time in a living body.
In contrast, such calcium phosphate compounds as hydroxyapatite and tricalcium phosphate are contained as main components of inorganic substances in living organisms and, therefore, possess outstanding bio-affinity manifesting safety to living organisms, ability to bind with bones, and ability to substitute for neoplastic bones. However, sintered articles of high-strength ceramics of calcium phosphate compound have never been produced.
In the circumstances, it is desirable to develop composite materials consisting of high strength ceramics such as sapphire and sintered alumina surfaces coated with a calcium compound for conferring bio-affinity.
As means of coating such bioceramics with the calcium phosphate compound, the flame spraying method, the sputtering method, the slurry method, etc. have been known to the art. The flame spraying method consists in fusing a powdered calcium phosphate compound in a flame of high temperature and spraying the resultant melt at a high speed on a substrate. Since this method requires use of an elevated temperature as described above, it has a disadvantage that the calcium phosphate compound yields to decomposition and induces alteration of the crystalline structure thereof. The sputtering method consists in sputtering the surface of a substrate with the calcium phosphate compound in a molten state. Since this method must be carried out under a high degree of vacuum, it inevitably suffers from poor productivity and high cost of production. The slurry method consists in spraying the substrate with a calcium phosphate compound in a slurry state, drying the applied layer of the slurry, and sintering the dried layer of slurry. This method has a disadvantage that the fastness of union between the substrate and the applied coating layer is not sufficient.